1. Field of the Invention
The present invention relates to an electrophotographic apparatus for printing images by an electrophotographic process, and to a developing device and a cleaning device used in the electrophotographic apparatus.
2. Description of the Related Art
In an electrophotographic apparatus, after the surface (photosensitive surface) of a photosensitive drum is charged by a charger at a predetermined potential (e.g. -600 V), the photosensitive surface is exposed by an exposing device in accordance with an image to be printed. Thereby, an electrostatic latent image is formed on the photosensitive surface of the photosensitive drum. The electrostatic latent image is developed by a developing device which applies toner on the photosensitive surface of the photosensitive drum in accordance with the electrostatic latent image. The developed toner image formed on the photosensitive surface of the photosensitive drum is transferred onto a printing paper sheet by a transferring device. Finally, the toner image is fixed on the paper sheet by a fixing device. The toner left on the photosensitive drum after transfer is removed by a cleaning device.
A known developing device, used in the above electrophotographic apparatus, is one which adopts a non-magnetic monocomponent developing system. According to this system, while non-magnetic toner is charged to have a predetermined polarity, the toner is adhered to a developing roller by an electromagnetic force due to the charge and the toner is conveyed onto the photosensitive drum by rotating the developing roller.
The developing device according to this system comprises a device casing which contains toner, a rotatable developing roller situated at that part of the casing which is opened to the photosensitive drum, and a toner restriction member for forming a thin toner layer on the peripheral surface of the developing roller and charging the toner.
Both side end portions of a roller shaft for supporting the developing roller are rotatably supported at the side walls of the device casing. One half of the circumferential surface of the developing roller is directed to the inside of the device casing, and the other half is exposed to the outside.
The toner restriction member, having a shape of e.g. blade, extends in the axial direction of the developing roller. In addition, the toner restriction member is situated above the developing roller in parallel, and it is put in contact with the peripheral surface of the developing roller. The toner restriction member is not provided at both end portions of the developing roller since the end portions of the roller are rotatably supported by the side walls.
The non-magnetic toner contained within the device casing is supplied to the developing roller by a supply roller situated on the inside of the developing device, and the non-magnetic toner is carried on the developing roller. The toner carried on the developing roller is conveyed as the developing roller is rotated, and the toner is put in contact with the photosensitive drum. While the toner is conveyed by the developing roller, it is passed between the developing roller and the toner restriction member. Thereby, a layer of toner adhered to the developing roller is thinned and charged. The toner is adhered to the developing roller by the electromagnetic force of the charge.
In this developing device, the toner is adhered to the peripheral surface of the developing roller only by the electromagnetic force acting between the peripheral surface of the developing roller and the toner. The amount of charge of the toner adhered to those portions of the developing roller located in the longitudinal direction of the roller, where the toner restriction member is not provided, is low. Thus, the electromagnetic force of the toner, adhered to the ends of the developing roller, is low.
Thus, the toner on both end portions of the developing roller, where the toner restriction member is not present, may flow off the end faces of the developing roller and escape out of the device casing of the developing device through a gap between the end face of the developing roller and the side wall of the device casing. If the toner escapes from the developing device, the toner can flow into the body of the apparatus (e.g. facsimile), including the electrophotographic apparatus or printing device, and will contaminate the inside of the apparatus.
In order to solve the above problem, there is known a conventional technique as shown in Japanese Patent Publication (KOKOKU) JP-A 2-26228. According to this technique, a lubricating seal material and a non-rotatable member are provided at each end of the developing roller. The two lubricating seal materials and two non-rotatable members have cylindrical shapes of the same diameter as the developing roller. The lubricating seal materials and non-rotatable members are loosely fitted on the shaft of the developing roller, and these components constitute a single cylindrical body. The non-rotatable members are positioned in close contact with the side walls of the device casing, and even if the developing roller rotates, the non-rotatable members do not rotate. The lubricating seal material is formed by attaching a lubricating film to an elastic member, and it has elasticity and lubricating properties. Thus, the lubricating seals are put in contact with the end portions of the developing member and non-rotatable members in good condition, while not preventing the rotation of the developing member.
According to this structure, escape of toner from a gap between the end face of the developing roller and the device casing can be prevented to some extent. However, with this structure, a gap is formed between the non-rotatable members and the toner restriction member, and therefore toner present at both end portions of the developing roller cannot be completely prevented from flowing off the end faces of the developing roller.
On the other hand, the cleaning device comprises a waste toner tank, and a blade attached to the waste toner tank so as to be in contact with the photosensitive drum. In the cleaning device, toner left on the photosensitive drum after transfer is removed by the blade and put in the waste toner tank.
In the cleaning device, a gap is formed between the waste toner tank and the photosensitive drum. Thus, there is a possibility that toner contained in the waste toner tank could escape from the waste toner tank through the gap between the waste toner tank and the photosensitive drum. If the toner escapes from the waste toner tank, it will flow out into the inside of the apparatus (e.g. facsimile) containing the electrophotographic apparatus or printing device and contaminate the inside of the apparatus.